The present invention relates to a damper disc for use as a clutch disc in an automobile, an agricultural machine or an industrial machine as well as a damper in a driving system of a boat and the like.
Japanese Utility Model application 57-10387 (U.S. patent application Ser. No. 421,338) has disclosed a damper disc in which compressible coil springs are disposed in series between an input member and an output member. In such disc, a spring seat or seats are interposed between the springs disposed in series in a set of openings of the input and output members. However, in this structure, there is a difference between the force applied to radially inner portions (with respect to the radial direction of the disc) of the springs and the force applied to the radially outer portions of the springs, when the springs are compressed, because the direction of the surfaces of the spring seats to which the springs are seated does not change with respect to the radial direction of the disc after the compression of the springs. This difference of the forces or loads may decrease durability of the springs. Further, the compressed springs may protrude radially outwardly and contact the edge of the opening. This contact and the friction force caused thereby deteriorates a damping characteristic of the disc, so that noises in a drive system, such as a transmission, can not be absorbed effectively.